It’s one of the reddest states in the nation and a leader in hydraulic fracturing, or “fracking,” which Sanders calls “a disaster for the planet.”

Yet Sanders’ Oklahoma City rally Sunday marked the democratic socialist’s second visit in one week to the state. Oklahoma is one of 11 states that will vote along with American Samoa on Super Tuesday and one of five where Sanders believes he has a strong chance of winning in his effort to secure the Democratic Party's nomination for president.

“On Tuesday, Oklahoma can play a very important role in moving this country forward to a political revolution. Let’s do it,” he told a crowd of more than 6,000.

Fresh off a large victory Saturday in the South Carolina primary, Sanders’ rival Hillary Clinton holds a 9 percentage-point lead in Oklahoma in a RealClearPolitics average of two polls this month. But the Sanders campaign believes his message about a rigged economy held in place by a corrupt campaign-finance system will resonate here.

“Oklahoma is a place where there is a tremendous amount of outsider, anti-establishment sentiment in the electorate and the electorate at large, by the way,” said Tad Devine, Sanders' senior media adviser.

At the rally, Sanders, the independent U.S. senator from Vermont, railed against Wall Street’s “enormous power” and called for a government that works for working families and not just the wealthiest Americans. He highlighted Clinton’s paid Wall Street speeches and called again for her to release transcripts.

“This campaign is gaining momentum because instead of listening to people who contribute to super PACs and billionaires, we are listening to the American people, and we are listening to you,” Sanders said.

He also pledged to tackle climate change, an issue he noted “puts me at odds with your political leadership.” Sen. James Inhofe, a member of Oklahoma’s entirely Republican congressional delegation, notoriously has referred to climate change as “a hoax.”

“We have a moral obligation to leave this planet in a way that is healthy and habitable,” Sanders said.

Sanders didn’t speak about fracking at Sunday’s rally, but in a fundraising email Friday, he specifically highlighted Oklahoma’s rash of earthquakes that many believe are linked to wastewater from fracking being injected into underground wells along fault lines. The Oklahoma Corporation Commission has told oil and gas companies to reduce wastewater in underground wells to curb the problem.

Sanders has launched a new television ad in Minnesota and Colorado about his stance against fracking. The campaign is using other ads in Oklahoma, where strategists believe he still needs to be introduced to voters, but they think the fracking issue will have a powerful impact here, as well.

Friday, Sanders targeted Clinton for holding a “high-dollar fundraiser” in January at a hedge fund, Franklin Square Capital, that invests in fracking, and he challenged her ability to tackle climate change as a result. Sanders supports a ban on fracking and has called for a moratorium on fossil fuels on public lands.

“Just as I believe you can’t take on Wall Street while taking their money, I don’t believe you can take on climate change effectively while taking money from those who would profit off the destruction of the planet,” Sanders wrote.

Clinton wants to move away from fossil fuels, including gas, but she said in October she sees gas as “useful bridge” to renewable alternatives. Her campaign says her plan to address climate change includes ways to make natural gas production safer.

“Hillary believes strongly that we need to make America the clean energy superpower of the 21st century — and that climate change is too big a problem to wait for Republicans in Congress to pass new legislation,” said Zac Petkanas, a campaign spokesman.

Concern about fracking and earthquakes in Oklahoma has been bipartisan, and many also are concerned about its effect on the environment, said Michael Crespin, a University of Oklahoma associate political science professor.

“Fracking is an issue where Sen. Sanders can differentiate himself from Secretary Clinton since she has expressed support for the natural gas sector,” Crespin said. “The voters who support Sanders’ other more liberal policies would also likely support his strong stance on fracking.”

At the Oklahoma City rally, Dillon Turner, 29, said Sanders’ position on the need for campaign finance reform is most important to him because “I think our democracy is in danger.”

But Turner, a marketing specialist at a company with ties to the oil and gas industry, also supports Sanders’ stance on fracking. He thinks Sanders would place a higher priority on addressing climate change than Clinton, who he said was slow to oppose the Keystone XL pipeline.